1. Field of the Invention
The present invention relates to a forging method and apparatus for forming helical gears, and more particularly to an improved cold forging method and apparatus for forming gears, such as helical gears, by pressing a stock into a helical mold.
2. Description of the Related Art
Conventionally, a helical gear, formed through cold forging, is directly usable without post-treatment of a gear portion thereof, leading to considerable economic benefit.
In the case of forming the helical gear by cold forging, however, it is difficult to form various helical gears having different helix angles with high accuracy since heretofore there has been given no consideration to the helical angle. Of course, although some products show high accuracy, it is insufficient to effectively deal with a requirement of producing helical gears increasingly being diversified.
Considering the conventional configuration of a forging apparatus for forming a helical gear, it comprises: a gear die having a gear teeth forming section defined at the inner circumference thereof for forming helical gear teeth; and a collar die integrally formed at an upper end of the gear die.
The conventional forging apparatus further comprises: a lower die located below the gear die; a punch located above the collar die for pushing a stock into the collar and gear dies; and a knock-out located below the lower die for discharging the molded stock to the outside.
When using the above described helical gear forging apparatus, due to a relative circumferential rotational force produced between the punch and the gear die and the integral structure of the gear die and the collar die, it is impossible that the stock rotates in a circumferential direction of the gear die relative to the gear die when it is pushed into the gear die.
For this reason, when gear teeth are formed on the outer circumference of the metal stock, the stock is inevitably displaced in an axial direction, disadvantageously causing lead gaps between the respective gear teeth formed in the gear die.
Such lead gaps exert an excessive stress on either side of the angled tooth of the stock inside the gear die, resulting in a pressure difference on toothed portions of the gear die and elastic restoration force on either side of the tooth of the resulting product.
This becomes a factor of adhesion and wear on the toothed portions of the die, and even damages the toothed portions.